Network users expect high reliability for networks. Network controllers executing various applications communicate with network elements such as switches, routers, hubs, bridges, gateways and servers to set up virtual or overlay networks with appropriate routing tables, MAC (media access control) addresses, etc. In some systems, when a network controller fails, the network elements are migrated to a new network controller so that the network(s) can continue running. But, this may involve resetting a new network controller, starting with default states and setting up new states for the network elements, and attendant delays and disruption to network service. Downtime for the new network controller is problematic. It is within this context that the embodiments arise.